1. Technical Field
The present invention relates to a multi-gap type rotary electric machine which is applicable to various uses, such as industrial uses and vehicle uses and in particular is preferred to be used in a drive motor for hybrid vehicles.
2. Related Art
As small and high-power motors based on conventional art, IPM motors (interior permanent magnet motors) are well known. The IPM motors can use reluctance torque that is a core attractive force, in addition to magnet torque that is generated by magnets. The IPM motors include double-stator motors in which stators are arranged in radially inside and radially outside of the rotor.
For example, a patent document JP-A-2008-302789 discloses a double-stator motor. In this double-stator motor, permanent magnets are embedded in the rotor so as to be located radially inward thereof, being opposed to the inner stator, and also embedded in the rotor so as to be located radially outward thereof, being opposed to the outer stator. The rotor also has salient poles (rotor core portions) each of which is formed between circumferentially adjacent magnets.
However, the motor disclosed in the patent document JP-A-2008-302789 suffers from a problem of not being able to increase power density for the reasons set forth below.
a) The stator winding is a short-pitch winding. Therefore, the pole pitch of the rotor does not coincide with the pole pitch of the magnetic field generated by the stator windings. Therefore, the reluctance torque cannot be fully used.
b) The surface of each of the salient poles of the rotor is concaved. Specifically, the inner peripheral surface of each of the inner salient poles and the outer peripheral surface of each of the outer salient poles of the rotor are concaved. Therefore, magnetic resistance is increased and the reluctance torque cannot be fully used.
c) The outer magnetic circuit is ensured to have a high rate of the reluctance torque by increasing the outer-salient-pole width relative to one pole pitch of the rotor. However, this increases the length of the magnetic path and accordingly increases the magnetic resistance, resulting in decreasing the reluctance torque. Further, since the increase of the salient-pole width necessarily decrease the magnet width, the magnet torque cannot be fully used as well.
d) Further, due to the increase of the outer-salient-pole width of the rotor, the rotor yoke, in which the magnetic path is shared between the outer and inner magnetic circuits, is unavoidably saturated with the magnetic flux supplied from the outer salient poles to the rotor. As a result, torque is decreased in the inner magnetic circuit as well which is preferred to have a short magnetic path compared to the outer magnetic circuit and to increase the rate of the reluctance torque.